In the field of radio communication, there has been actively employed in recent years MIMO (multiple-input and multiple-output) technology, in which speed and quality of signal transmission are improved by carrying out transmission/reception using a plurality of antennas on the transmitter side and receiver side. MIMO technology includes SU-MIMO (single user MIMO) for a single user (receiver), and MU-MIMO (multiple user MIMO) for a plurality of users (receivers).
Further, there is considered (for example, Patent Document 1) the use of a massive-MIMO transmission scheme that uses a large number of antenna elements (for example, 100 elements or more) so as to achieve a further increase in speed and a reduction in interference in signal transmission in a high-frequency band (for example, 10 GHz or higher), which also enables miniaturization of antennas and in which a wide bandwidth can be attained.
With massive-MIMO, there can be achieved advanced beamforming (BF) by use of a large number of antenna elements, compared to conventional MIMOs. Beamforming is a technology for controlling a directionality and shape of beams (for example, transmission beams corresponding to transmission antennas, reception beams corresponding to reception antennas) by controlling a plurality of antenna elements. With MIMO, phase and amplitude can be controlled for each antenna element, thus the larger the number of antenna elements used, the greater the degree of freedom of beam control.
As one mode of beamforming, fixed beamforming is exemplified. In fixed beamforming, a beamforming weight (fixed beam) to be used is selected from among a plurality of beamforming weights prepared in advance. In fixed beamforming, beamforming that controls fixed beams and coding that achieves compensation for multiplexing between a plurality of streams (transmission-side precoding and reception-side postcoding) are carried out separately.